1. Field of the Invention
The present invention relates to image forming methods and apparatus to inject a liquid drop including color material according to an image signal to form an image on a transfer medium, and more particularly relates to image forming methods and apparatus that transfer an image formed by liquid drops having been increased in viscosity onto a recording medium and that separate the recording medium from the transfer medium.
2. Related Art
Ink jet printers have become widely used with a recent improvement in the performance not only for a small volume recording but also for a large volume recording such as ones for use in an office or for incorporation in a production equipment. With such expansion of the field of use of ink jet printers, a demand has increased for recording an image on a sheet of high quality plain paper with less blotting. In ink jet printers, formation of an image on a sheet of plain paper without blotting has been one of most important technical challenges, demand for which has recently increased more than ever.
For formation of an image on a sheet of plain paper without blotting, various attempts have been made. In particular, a technology to transfer an image onto a sheet of plain paper used as a recording medium via a transfer medium has been regarded as one of the promising technologies, and developments of such a technology have been vigorously pursued.
For example, Japanese Patent Laid-open publications Nos. 6-293178 and 7-089067 describe methods of solving blotting of an image on a sheet of plain paper serving as a recording medium. In the methods, an image is once formed with ink jet liquid drops on a transfer medium, and the image is then transferred to a sheet of plain paper when the ink jet liquid drops have changed, through phase transition, for example by being heated, to have a viscosity suitable for being transferred.
However, in the methods described in the JP Laid-open publications No. 6-293178 and 7-089067, a surface active agent is adhered to the transfer medium in advance for increasing the wettability of a transfer medium. Therefore, it takes a certain time for liquid drops, forming an image on the transfer medium, to change to have a viscosity suitable for the transfer, for example by being heated, and the image on the transfer medium tends to blot during that time. In particular, blotting is remarkable in solid parts of an image. Because of such time for waiting for liquid drops to change to have a viscosity suitable for transfer, increasing the printing speed, for example in a line printer, is limited.
Further, for solving the above-described problem in the methods described in JP Laid-open publications 6-293178 and 7-89067, the applicant of the present invention has proposed in Japanese Patent Laid-open publication No. 11-188858 a method in which powder having an absorbing property is adhered onto a transfer medium and the viscosity of ink liquid drops forming an image on the transfer medium is increased by the powder being absorbed by the ink liquid drops in a short time. The ink liquid drops as an image are transferred to a sheet plain paper utilizing increased viscosity of the ink liquid drops, and thereby image blotting in the sheet of plain paper is avoided. This method enables instantly obtaining a clear image having less blotting on a sheet of plain paper. In particular, if liquid ink drops having increased viscosity can be completely transferred to a recording medium, necessity of cleaning a surface of the transfer medium is eliminated, and thereby the transfer mechanism can be simplified and earlier deterioration of the transfer medium can be prevented, which are convenient.
However, it has been revealed by the inventors of the present invention, through minute observation of an image transferred onto a recording medium, that even an image which appears to be satisfactory has some inferior parts. Specifically, a phenomenon has been revealed that some parts of an image, having been transferred onto a recording medium, are omitted due to insufficient viscosity of the image.
Further, in the methods of JP Laid-open publications Nos. 6-126945 and 7-82516 and JP No. 2743151 which use a transfer medium as in the method of JP Laid-open publication No. 11-188858, a problem is known that some parts of an image are not transferred when liquid drops forming the image, which have been increased in the viscosity, are not well caught in the fibers of a sheet of paper serving as a recording medium.
In addition to the above-described problem relating to viscosity of liquid drops, another problem is known that uneven image transfer occurs if contact between a sheet of paper and a transfer medium is insufficient when transferring an image.
Still furthermore, a problem is known that inadequate separation of a recording medium from a transfer medium remarkably influences the quality of a transferred image as in insufficient transfer of the image.
The present invention has been made in view of the above-discussed and other problems and addresses the above-discussed and other problems.
Accordingly, preferred embodiments of the present invention provide a novel image forming method and a novel image forming apparatus, in which good transfer of an image onto a recording medium from a transfer medium is achieved, ink liquid drops having been increased in the viscosity are sufficiently tangled with fibers of paper serving as the recording medium such that occurrence of partially uneven transfer of the image is avoided, and the performance of image fixing on the recording medium is improved.
Further, preferred embodiments of the present invention provide a novel image forming method and a novel image forming apparatus that achieve good contact between a recording medium and a transfer medium when transferring an image from the transfer medium to the recording medium, such that ink liquid drops having been increased in the viscosity are sufficiently tangled with fibers of paper serving as the recording medium, and thereby partially uneven image transfer is avoided and image fixing performance is improved.
Still furthermore, preferred embodiment of the present invention provide a novel image transfer method and a novel image transfer device that transfer an image to a recording medium from a transfer medium by pressing the recording medium to the transfer medium and that then smoothly separate the recording medium from the transfer medium.
According to a preferred embodiment of the present invention, a method of forming an image includes steps of causing a material, that increases a viscosity of liquid drops by contact with the liquid drops, to adhere to a transfer medium, causing a liquid drop to contact the material according to an image signal such that an image is formed with the liquid drop having been increased in viscosity by contact with the material, and transferring the image formed by the liquid drop having been increased in viscosity to a recording medium. Viscosity of a liquid drop when increased on the transfer medium by contact with the material is set such that the liquid drop adheres to the recording medium and such that the liquid drop is transferred to the recording medium without being divided into a part remaining on the transfer medium and another part being transferred to the recording medium. By the above-described image forming method, good image transfer is realized and thereby an image having no blotting is obtained.
According to the invention, in the above-described method, viscosity of a liquid drop when increased by contact with the material may be between 10,000 cps (centipoise) and 200,000 cps. By setting viscosity of a liquid drop when increased by contact with the material in such a range, an image of good quality is obtained.
Further, an interval of the material to adhere to the transfer medium may be made smaller than a diameter of the liquid drop when the liquid drop contacts the transfer medium. Thereby, it never occurs that some liquid drops are not increased in the viscosity, and therefore uneven transfer of an image is avoided.
Furthermore, in the step of causing the material to adhere to the transfer medium, the material may be formed into an aggregation that is movable in a lump before adhering to the transfer medium, and when the material adheres to the transfer medium, an interval of the material to adhere to the transfer medium may be made smaller than a diameter of the liquid drop when the liquid drop contacts the transfer medium. Thereby, because a sufficient amount of the material adheres to the transfer medium, even when an image is formed by a large amount of liquid drops, for example as when the image includes a solid part in which more than two colors are overlapped, apprehension for insufficient viscosity of the liquid drops is avoided. Further, because an adhering interval of the aggregations is smaller than a diameter of a liquid drop when the liquid drop contacts the transfer medium, it never occurs that some liquid drops are not increased in the viscosity. Thereby, uneven transfer of an image is more securely avoided.
According to another preferred embodiment of the present invention, an image forming apparatus includes a transfer medium, and a material forming device configured to cause a material, that increases a viscosity of liquid drops by contact with the liquid drops, to adhere to the transfer medium. An image forming device causes a liquid drop to contact the material according to an image signal such that an image is formed with the liquid drop having been increased in viscosity by contact with the material. A transfer device transfers the image formed with the liquid drop having been increased in viscosity onto a recording medium. A setting device sets viscosity of the liquid drop when increased on the transfer medium by contact with the material such that the liquid drop adheres to the recording medium and such that the liquid drop is transferred to the recording medium without being divided into a part remaining on the transfer medium and another part being transferred to the recording medium. Good image transfer is realized by the above-described image forming apparatus, so that a good image having no blotting is obtained.
According to the invention, in the above-described image forming apparatus, the viscosity setting device may be the material forming device. Thereby, the image forming apparatus is simplified.
Further, the material forming device may include a device configured to cause the material to adhere to the transfer medium at an interval smaller than a diameter of the liquid drop when the liquid drop contacts the transfer medium. Accordingly, it never occurs that some liquid drops are not increased in the viscosity, and thereby uneven transfer of an image is avoided.
Furthermore, the material forming device may further include an aggregation forming device configured to form the material into an aggregation that is movable in a lump, and when the material, after having been formed into the aggregation, is caused to adhere to the transfer medium, an interval of the material to adhere to the transfer medium may be set to be smaller than a diameter of the liquid drop when the liquid drop contacts the transfer medium. Thereby, because a sufficient amount of the material adheres to the transfer medium when the material is applied onto the transfer medium, even when an image is formed by a large amount of liquid drops, for example as when the image includes a solid part in which more than two colors are overlapped, apprehension for occurrence of insufficient viscosity of the liquid drops is avoided. Further, because an adhering interval of the aggregations is smaller than a diameter of a liquid drop when the liquid drop contacts the transfer medium, it never occurs that some liquid drops are not increased in the viscosity. Thereby, uneven transfer of an image is more securely avoided.
Still furthermore, the aggregation forming device may include a concave at a surface thereof facing the transfer medium and be configured to form the aggregation by containing the material in the concave. By making an interval of the concave portions smaller than a liquid drop diameter when the liquid drop contacts the transfer medium, an interval of the material to adhere to the transfer medium is securely made smaller than the liquid drop diameter.
Further, the aggregation forming device may be made of a urethane sponge, such that the construction is simplified and thereby the cost is reduced.
Further, the image forming apparatus may include in a vicinity of the aggregation forming device a device to make the aggregation uniform. Because the aggregation is made uniform by the device, occurrence of image blotting and penetration through a recording medium at some portions of an image is avoided, and thereby en extremely good image can be obtained.
According to another preferred embodiment of the present invention, an image forming apparatus includes a transfer medium, a material forming device configured to cause a material, that increases a viscosity of liquid drops by contact with the liquid drops, to adhere to the transfer medium, an image forming device configured to cause a liquid drop to contact the material according to an image signal such that an image is formed with the liquid drop having been increased in viscosity by contact with the material, and a transfer device configured to transfer the image formed with the liquid drop having been increased in viscosity onto a recording medium. The transfer device includes a transfer medium support device configured to support the transfer medium, and a recording medium support device configured to support the recording medium, and a hardness of the transfer medium support device is made different from a hardness of the recording medium support device. By making the transfer medium support device and the recording medium support device different in hardness, a transfer nip formed between the transfer medium support device and the recording medium support device is formed in a shape which is not flat, i.e., in a curved shape, and thereby the liquid drops forming an image on the transfer medium more closely contact a recording medium, such that uneven transfer of the image is hard to occur.
The transfer medium support device may be configured so as to convey the transfer medium and the recording medium support member may be configured so as to convey the recording medium. Thereby, the image forming apparatus may be simplified.
Alternatively, the transfer medium support device and the recording medium support device may be made different in diameters, or the transfer medium support device and the recording medium support device may include elastic members which are different in thickness. Thereby, the transfer nip is formed in a curved shape, such that uneven transfer of an image is similarly hard to occur.
According to another preferred embodiment of the present invention, an image transfer apparatus includes a transfer medium and a pressing device that is configured to press a recording medium brought in contact with the transfer medium such that the image is transferred onto the recording medium, for use in an image forming apparatus having a material forming device configured to cause a material, that increases a viscosity of liquid drops by contact with the liquid drops, to adhere to a transfer medium of the image transfer device and an image forming device configured to cause a liquid drop to contact the material according to an image signal such that an image is formed with the liquid drop having been increased in viscosity by contact with the material. A surface of the transfer medium and a surface of the pressing device are moved at different speeds, and the recording medium is moved by movement of the transfer medium. Because the pressing device causes a rubbing force to act on the recording medium being conveyed along the transfer medium, the recording medium closely contacts the transfer medium such that an image formed with liquid drops having been increased in viscosity is effectively pressed into paper fibers of the recording medium so as to be firmly entangled with the paper fibers. Accordingly, occurrence of partially inferior image transfer is avoided.
According to the invention, the surface of the pressing device may include fluorine resin. Thereby, when an image formed with liquid drops having been increased in viscosity is pressed by the pressing device so as to be effectively entangled with paper fibers of a recording medium, the pressing device and the recording medium slide smoothly relative to each other such that transfer performance is improved.
Further, the pressing device may be configured to stop when transferring an image. Thereby, construction of the transfer apparatus may be simplified. Further, shape of a portion of the pressing device contacting a recording medium can be freely determined and therefore it is relatively easy to realize a relatively wide nip width.
Furthermore, the pressing device may be configured so as to rotate and to move in a substantially same direction as the transfer medium when transferring an image. Thereby, resistance to a recording medium when the recording medium is conveyed in a downstream direction in a rotation direction of the transfer medium is small, so that the recording medium is securely conveyed. Also, insertion of a recording medium toward the pressing device (roller) is relatively easier than when the pressing device is at a standstill. Further, when a leading edge of a recording medium contacts either the pressing device or the transfer medium, a conveying force to convey the recording medium in a downstream direction in a transfer medium conveyance direction acts on the leading edge of the recording medium, so that insertion of the recording medium is facilitated.
Still furthermore, the transfer medium and the pressing device may be configured so as to be driven by a same driving device. Thereby, controlling the transfer medium and the pressing device to operate in a synchronized manner is facilitated. Accordingly, the transfer apparatus as described above may be effectively used in an image forming apparatus in which a transfer medium is intermittently driven or a moving speed of the transfer medium is changed according to a change of the operating mode.
Alternatively, by configuring the transfer medium and the pressing device so as to be driven by separate driving devices, adjustment of a relationship of moving speeds between the transfer medium and the pressing device is facilitated. The relationship can be controlled according to the recording medium, e.g., according to the kind of recording paper and thickness of the paper, or according to the environmental conditions, so that good image transfer is enabled.
According to another preferred embodiment of the present invention, an image forming apparatus includes a transfer medium, and a material forming device configured to cause a material, that increases a viscosity of liquid drops by contact with the liquid drops, to adhere to the transfer medium. An image forming device causes a liquid drop to contact the material according to an image signal such that an image is formed with the liquid drop having been increased in viscosity by contact with the material, and a transfer device transfers the image formed with the liquid drop having been increased in viscosity onto a recording medium. The transfer device is configured so as to form a transfer nip, where the image is transferred onto the recording medium, in a curved shape. Because the transfer nip is curved, a rubbing force is generated between the transfer medium and the recording medium, and thereby the recording medium closely contacts the transfer medium such that the image formed with the liquid drops having been increased in viscosity is effectively pressed into paper fibers of the recording medium so as to be firmly entangled with the paper fibers. Accordingly, occurrence of partially inferior image transfer is avoided.
According to another preferred embodiment of the present invention, a method of forming an image includes steps of causing a material, that increases a viscosity of liquid drops by contact with the liquid drops, to adhere to a transfer medium, causing a liquid drop to contact the material according to an image signal such that an image is formed with the liquid drop having been increased in viscosity by contact with the material, and transferring the image formed by the liquid drop having been increased in viscosity to a recording medium brought into contact with the transfer medium by pressing the recording medium with a pressing device. According to the invention, in the transferring step, surfaces of the transfer medium and the pressing device are moved at different speeds, and the recording medium is moved by movement of the transfer medium. Because the pressing device presses the recording medium at the side not contacting the image and rubs the recording medium, the contact of the pressing device and the recording medium is remarkably improved so that the image formed with the liquid drops having been increased in viscosity is effectively pressed into paper fibers of the recording medium so as to be firmly entangled with the paper fibers. Accordingly, occurrence of partially inferior image transfer is avoided.
According to another preferred embodiment of the present invention, a method of forming an image includes steps of causing a material, that increases a viscosity of liquid drops by contact with the liquid drops, to adhere to a transfer medium, causing a liquid drop to contact the material according to an image signal such that an image is formed with the liquid drop having been increased in viscosity by contact with the material, transferring the image formed by the liquid drop having been increased in viscosity to a recording medium, and separating the recording medium from the transfer medium. According to the invention, in the separating step the recording medium is separated by passing a curvature portion of the transfer medium. Thereby, the recording medium is securely separated from the transfer medium.
According to the invention, before the recording medium passes the curvature portion of the transfer medium, in the transferring step the image on the transfer medium and the recording medium are brought into contact with each other and are pressed so that the image is transferred to the recording medium. Accordingly, the image is securely transferred onto the recording medium, and further the recording medium is securely separated from the transfer medium.
According to another preferred embodiment of the present invention, an image forming apparatus includes a transfer medium, a material forming device configured to cause a material, that increases a viscosity of liquid drops by contact with the liquid drops, to adhere to the transfer medium, and an image forming device configured to cause a liquid drop to contact the material according to an image signal such that an image is formed with the liquid drop having been increased in viscosity by contact with the material. According to the invention, the transfer medium includes a transfer position to transfer the image formed with the liquid drop having been increased in viscosity onto a recording medium and a separation position to separate the recording medium from the transfer medium, and a curvature is formed in the transfer medium at the separation position of the transfer medium. Due to the curvature formed in the transfer medium at the separation position, the recording medium is securely separated from the transfer medium.
According to the invention, the radius of curvature formed in the transfer medium at the separation position is preferably between about 1.25 mm and about 15 mm, so that a recording medium can be securely separated from the transfer medium.
Further, the radius of curvature formed in the transfer medium at the separation position may be between about 1.25 mm and about 7 mm, so that a recording medium can be more securely separated from the transfer medium. Specifically, when a recording medium carries an image at a leading edge of the recording medium, the recording medium more firmly contacts the transfer medium as compared when the recording medium does not carry an image at a leading edge thereof. By making the curvature formed in the transfer medium at the separation position smaller, even in such a case, the recording medium can be securely separated from the transfer medium. Further, when an image forming apparatus is configured such that a blank part is formed at a leading edge of a recording medium for securely separating the recording medium from a transfer medium, by sufficiently examining a relationship between the transfer position of the transfer medium and the curvature formed in the transfer medium at the separation position, the blank part required at a leading edge of a recording medium can made less.
Further, a pressing device to press the transfer medium at the transfer position is provided upstream of the separation position of the transfer medium where the curvature is formed in the transfer medium, in a conveying direction of the recording medium. With provision of such a pressing device, good image transfer and good separation of a recording medium are both achieved.
Furthermore, when support members supporting the transfer medium at the transfer position and the separation position respectively include rollers, a radius of the roller supporting separating position may be made smaller than a radius of the roller supporting the transfer medium at the transfer position. In order to achieve good transfer of an image, a transfer nip for the transfer must be wide. Therefore, a roller having a relatively large diameter is used for the support member supporting the transfer medium at the transfer position. On the other hand, in order to achieve good separation of a recording medium from the transfer medium, a curvature formed in the transfer medium at the separation position must be small. Therefore, a roller having a relatively small diameter is used for the support member supporting the transfer medium at the transfer position. Thereby, both the image transfer performance and the reliability of separating a recording medium from the transfer medium have been improved.
Further, a support member supporting the transfer medium at the transfer position and a support member supporting the transfer medium at the separation position may be formed in an integral body. Thereby, while good image transfer and good separation of a recording medium are both achieved, the apparatus can be simplified.
Furthermore, a plurality of transfer positions may be provided, so that the image transfer performance is further enhanced.
Further, according to the invention, a support member supporting the transfer medium at the separation position and a support member supporting the transfer medium at the transfer position may be separate. Thereby, the image transfer performance and the separation performance of a recording medium can be respectively improved by individually optimizing a transfer nip formed by the support member supporting the transfer medium at the transfer position and a pressing device pressing a recording medium at the transfer position and a curvature formed in the transfer medium at the separation position by the support member supporting the transfer medium at the separation position.
According to another preferred embodiment of the present invention, an image forming apparatus includes a transfer medium, a material forming device configured to cause a material, that increases a viscosity of liquid drops by contact with the liquid drops, to adhere to the transfer medium, and an image forming device configured to cause a liquid drop to contact the material according to an image signal such that an image is formed with the liquid drop having been increased in viscosity by contact with the material. A transfer device is configured to transfer the image formed with the liquid drop having been increased in viscosity onto a recording medium, and a separation device is configured to separate the recording medium from the transfer medium. According to the invention, when the image forming apparatus is such that an image forming operation by the image forming device and an image transferring operation by the image transfer device are intermittently performed at a same time, a plurality of pressing devices for image transfer are arranged at an interval different from an integer times of an interval the transfer medium is intermittently moved. When an image forming apparatus is configured such that an image forming operation by an image forming device and an image transferring operation by an image transfer device are intermittently performed at a same time, uneven transfer of an image is caused in the image due to intermittent movement of the transfer medium. More particularly, when an image forming operation is performed by the image forming device for formation of an image on the transfer medium, the transfer medium stops while one line of the image is being formed, and after completion of one line of the image, the transfer medium is moved for formation of a next line of the image. Therefore, during that time when the transfer medium is stopped, a same portion of the image which is being transferred at a transfer position of the transfer medium continues to be pressed, and thereby is transferred differently from another portion of the image which has been transferred while the transfer medium is moving. By arranging a plurality of pressing devices at an interval different from an integer times of the interval the transfer medium is intermittently conveyed, the above-described uneven transfer of an image is avoided.